Co-targeting SRC overcomes resistance to BRAF inhibitors in colorectal cancer

BRAF^V600E mutations occur in ∼10% of colorectal cancer (CRC) patients, leading to poor prognosis. Although BRAF-targeted therapy is ineffective in CRC, adding EGFR inhibitors (EGFRi) improves efficacy, yet patient survival remains suboptimal. This study explores SRC as a key mediator of resistance to BRAF inhibitors (BRAFi) in preclinical BRAF^V600E CRC models, and its potential as a therapeutic target.

We studied SRC using BRAF-mutated and wild-type CRC cell lines with CRISPR/Cas9 knockouts and lentiviral overexpression. We tested SRC, BRAF, EGFR, and JNK targeting drugs, assessing protein expression, cell viability, proliferation, migration, apoptosis, and cell cycle. CRC cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) models were established for in vivo studies.

SRC regulates proliferation, clonogenicity, migration and mediates BRAFi resistance in BRAF^V600E CRC, regardless of microsatellite instability. Depletion or inhibition of SRC sensitized cells to BRAFi. Combined SRC and BRAF inhibition demonstrated a synergistic antitumor effect, reducing cell viability and inducing apoptosis and cell cycle arrest in cell lines and PDXs. The JNK/c-Jun pathway contributes to adaptive resistance, and its inhibition enhances the effects of dual SRC and BRAF inhibition.

These findings identify new therapeutic targets for clinical trials, potentially improving outcomes for this high-risk CRC subgroup.